The present invention relates to a turbocharger for use in an internal combustion engine, and, more particularly, to a turbocharger including a multi-stage turbine.
An internal combustion engine may include one or more turbochargers for compressing a fluid which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor which is driven by the turbine. The compressor receives the fluid to be compressed and supplies the fluid to the combustion chambers. The fluid which is compressed by the compressor may be in the form of combustion air or a fuel/air mixture.
U.S. Pat. No. 3,044.683 (Woollenweber) discloses a fluid passage extending from the high pressure side of the compressor to the inlet side of a turbine. A spring loaded valve is disposed within the fluid passage and opens upon a high pressure condition within the compressor. The spring loaded valve thus merely acts to bypass some of the high pressure gas on an over pressure condition to the turbine of the turbocharger.
U.S. Pat. No. 5,724,813 (Fenelon et al.) assigned to the assignee of the present invention, discloses a turbocharger having a single stage compressor. A portion of the compressed gas from the single stage compressor may be recirculated to the outlet side of the turbine using controllably actuated valves. The control scheme utilizes only a single stage compressor.
U.S. Pat. No. 5,701,741 (Halsall) discloses a turbocharger having a single stage turbine driven by exhaust gas from an exhaust manifold. A bypass valve is fluidly connected at opposite ends with the inlet and outlet to the turbine. The valve may be actuated to bypass exhaust gas around the turbine. The rotational speed of the single stage compressor may thereby be adjusted.
Bypass systems as described above which bypass from the compressor to the turbine are primarily used to prevent a xe2x80x9csurgexe2x80x9d condition within the compressor, rather than adjust power inputs to the compressor. Bypass systems which bypass the entire turbine are used to control the power input to the compressor. Since the entire turbine is bypassed, however, the ability to control the power input to the compressor and thus the boost from the compressor is limited. That is, it may not be possible to selectively control the boost from the compressor over a relatively wide operating range.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, a turbocharger for an internal combustion engine is provided with a two stage turbine including a first turbine stage and a second turbine stage. A wastegate conduit is fluidly coupled with the two stage turbine. The wastegate conduit bypasses only a single one of the first turbine stage or second turbine stage. A valve is positioned in association with the wastegate conduit for controlling flow through the wastegate conduit. A compressor is coupled with and rotatably driven by the two stage turbine.
In another aspect of the invention, a method of operating a turbocharger in an internal combustion engine is provided with the steps of: providing a two stage turbine including a first turbine stage and a second turbine stage; fluidly coupling a wastegate conduit with the two stage turbine so as to bypass only a single one of the first turbine stage and the second turbine stage; providing a compressor mechanically coupled with the two stage turbine; controlling a flow of exhaust gas through the wastegate conduit; and rotatably driving the compressor with the two stage turbine.